Syringes are one of medical devices that need lubricants for smooth sliding of the components. Disposable syringes made from a synthetic resin, as syringes used for general use, comprise a barrel, a gasket in tight contact with an inner surface of the barrel, and a plunger extending from the gasket towered the rear end of the syringe to slide the gasket. The syringes are used with the following method: the plunger is moved to the direction of the rear end of the barrel to fill the syringe with a drug solution, and the plunger is moved toward the tip of the barrel to discharge the drug solution charged in the syringe from the tip. Also, prefilled syringes, which are filled with drug solutions beforehand, are used with the following method: a plunger is moved toward the tip of a barrel to discharge the drug solution contained in the syringe.
The gasket used for these syringes is in tight contact with the inner surface of the barrel. The gasket is used to discharge the drug solution from the barrel while preventing leakage of the drug solution charged in the syringe and mixing of air bubbles, and is formed from an elastic material such as a synthetic rubber. The gasket has to slide in the barrel smoothly to discharge the drug solution, whereby in conventional disposable syringes, a silicone oil is applied as a lubricant to the inner surface of the barrel or the outer surface of the gasket.
However, the syringes are disadvantageous in that, when they are used for injection of a drug solution containing a drug having a surface activity, the silicone oil applied as a lubricant forms oil droplets on the inner surface of the barrel or the sliding friction of the gasket is. increased, whereby there has been a demand for a measure therefor. The generation of the oil droplets on the inner surface of the syringe is a problem to be solved in particular, because there is a possibility that the oil droplets mixed with the drug solution by separating from the inner surface of the syringe will be injected into a human body.
In regard to the problem caused by the contacting lubricant applied to the inner surface of the barrel or the outer surface of the gasket and the drug solution contained in the syringe, syringes with which the measures for solving the problem are heretofore known as follows: syringes having such a structure that a lubricant is blended with a material of a gasket and not applied to surfaces of the syringe or gasket (e.g., Patent Documents 1 and 2); syringes having such a shape that a gasket does not directly come into contact with a drug solution (e.g., Patent Document 3); syringes using a particular method for fixing a lubricant to a gasket, thereby making the lubricant less likely to fall off (e.g., Patent Documents 4 and 5); and syringes having such a structure that a lubricant is applied only to a necessary portion of the syringe to reduce a contact area between the lubricant and a drug solution (e.g., Patent Document 6).
However, these technologies require a drastic design change of structures from the conventional syringes or require only a small design change with insufficient effects. These technologies are not sufficient as a measure for using the syringes for injection of a surface-active drug solution without the problem, which is one of the applications of the syringes.
Patent Document 1:
Japanese publication Number Hei5-131029
Patent Document 2:
Japanese publication Number 2001-289326
Patent Document 3:
Japanese publication Number 2002-172166
Patent Document 4:
Japanese publication Number 2002-506694
Patent Document 5:
Japanese publication Number 2004-162761
Patent Document 6:
Japanese publication Number 2004-57819
Accordingly, an object of the present invention is to provide a syringe which can be designed and produced in the same manner as conventional syringes without a drastic design change, and can be used for injection of a drug solution having a surface activity without generation of oil droplets on the inner surface of the syringe and an increase of the sliding friction of the gasket.